The permeation of oxygen ions through ceramic ion transport membranes is the basis for the design and operation of high-temperature oxidation reactor systems in which permeated oxygen is reacted with oxidizable compounds to form oxidized or partially-oxidized reaction products. The practical application of these oxidation reactor systems requires membrane assemblies having large surface areas, flow passages to contact oxidant feed gas with the oxidant sides of the membranes, flow passages to contact reactant feed gas with the reactant sides of the membranes, and flow passages to withdraw product gas from the permeate sides of the membranes. These membrane assemblies may comprise a large number of individual membranes arranged and assembled into modules having appropriate gas flow piping to introduce feed gases into the modules and withdraw product gas from the modules. Ion transport membrane assemblies may be fabricated, for example, in either planar or tubular configurations.
The production of synthesis gas (syngas) in ion transport membrane (ITM) oxidation reactor systems combines the unit operations for oxygen separation and high-temperature syngas generation into a single process. In the ITM oxidation reactor system or ITM syngas reactor, oxygen selectively permeates across a mixed-conducting membrane from an oxygen-containing stream, e.g. air, on the cathode side of the membrane to subsequently react with reactants on the anode side of the membrane. Primary reactants may include oxygen, steam, hydrocarbons, pre-reformed mixtures of steam and hydrocarbon feed gas, hydrogen, carbon monoxide, carbon dioxide, and/or carbon dioxide-containing gas.
A number of exothermic and endothermic reactions occur in the process including partial oxidation, complete oxidation, steam reforming, carbon dioxide reforming, and water-gas shift to produce the synthesis gas product. ITM oxidation reactors typically operate in a narrow temperature range, for example, 700° C. to 1000° C. (1292° F. to 1832° F.). A description of a representative staged ITM reactor system and operation is given in U.S. Patent Application Publication No. 2008/0302013 A1 entitled “Staged Membrane Oxidation Reactor System”. This system can be operated to provide a stable ITM syngas process which may be controlled to operate at design conditions, including design production capacity and design feedstock conversion to valuable products, within the required temperature constraints.
An ITM syngas reactor system may be designed to yield a syngas product having a desired product composition and product flow rate wherein the system operates at a preferred feed hydrocarbon conversion. The design conditions are selected for efficient operation with a given feedstock to yield the specified product quality and production capacity over a satisfactory membrane operating life. For commercial and/or operational reasons, it may be necessary to operate the ITM reactor system at off-design or alternate conditions for certain time periods. For example, periods of turndown operation at reduced production rates may be needed due to lower requirements of the downstream syngas consumption process. In another example, changes in syngas composition may be required for specific operational reasons. Other situations can be envisioned in which off-design or alternate operation is required for varying time periods.
It is desirable to select the operating conditions used during periods of off-design or alternate operation to prevent or minimize damage to the membranes, to minimize potential reduction in membrane life, and to provide the desired syngas product quality at a desired efficiency.
There is a need in the art of synthesis gas generation by ITM oxidation reactor systems for effective, efficient, and reliable methods for operating and controlling the systems at off-design or alternate operating conditions. In particular, there is a need for off-design or alternate operational methods for ITM reactor systems having multiple stages or groups of stages arranged and operated in series. The embodiments of the invention disclosed and claimed herein provide off-design or alternate operating methods to address these needs.